Hob, Oven and Dishwasher Question

[bernithebiker]

I have one earth cable, at least 2.5mm, more like a 4mm.

If I route all three earths (hob, oven, dishy) through this one is that OK?

Thanks,

Berni

Oh, by the way, the hob instructions (hob comes without a cable) say that it is OK to use a 2.5mm cable (3 conductors of 2.5mm), which I find kind of weird as I would have thought a 4 or 6mm more appropriate given that it is rated at 6.3kW.

The hob has 3 live connectors and 2 neutrals. If using triple phase you can even go down to 1.5mm.......

 

[TrueBlue]

I thnk before you connect anything up, you should find out exactly what size of cables you have. You seem a bit unsure. It can sometimes be difficult to tell by looking.

 

[bernithebiker]

What is the best way to tell? With a micrometer? I have roughly measured the external diameter with a ruler which is almost 5mm, so I think 4mm is right.

The 2.5mm solid core that I bought can be bent fairly easily with fingers. My 5 conductor cable coming out of the wall needs pliers to bend it, so it must be larger than 2.5mm, thus 4mm, next size up?

In any case, with the 2 pairs together I know I have at least 5mm cable, quite possibly 8mm, with an earth of 4mm.

To reassure everyone! I will also be using individual trip switches for each appliance, housed in an IP 65 waterproof box. 32A for the hob, and 16A for the oven and dishy. In that way, I have double protection.

And even though the hob instruction say 2.5mm is OK, I'm going with 4mm (to link the hob to the wall).

 

[Pensdown]

Adam_151 posted this from TLC, it should help

1mm² CSA T&E has overall dimensions of 7.8mm x 4.25mm
1.5mm² CSA T&E has overall dimensions of 8.2mm x 5mm
2.5mm² CSA T&E has overall dimensions of 10.3mm x 6mm
4mm² CSA T&E has overall dimensions of 11.9mm x 6.25mm
6mm² CSA T&E has overall dimensions of 13.5mm x 7mm
10mm² CSAT&E has overall dimensions of 17.1mm x 10mm
16mm² CSA T&E has overall dimensions of 19.4mm x 10mm

 

[Steve]

How about this - use one pair for the hob (i.e. 4mm +ve, -ve and 20A fuse), one pair for the oven and dishwasher (i.e. 4mm on 20A fuse). As long as the cable is adequately protected - which it would be whether 4 or 2.5mm.

6kW for the hob, 5ish for the oven and dishwasher. If what you say re. the fuses is correct, then even if the hob pulls full power (about 24A) I should be OK, fusewise, as such a load would only be shortlived. Likewise for the oven and dishwasher (about 20A peak load).

In this way, I should be almost legal! I also intend to put individual switched fuses of either 10 or 16A inline with the oven and dishwasher for extra protection. A 13A plug and socket would do the job.

the trip switches aren't nessecary.

If you really must wire this as you say, Put both circuits on 20A MCBs. For the Hob, do as above - run the 4mm² to the control switch and then the hob. For the W/M and oven, run the cable to 2 FCUs with 13A fuses, or just 2 sockets. PLEASE stop talking about putting the 2 cables together - you have been told before, you cannot do this. And the cables aren't +ve and -ve. Those terms do not exist in AC theory, only DC. For AC, the terms are "phase" or "live" and "neutral"

 

[ban-all-sheds]

OK I take your point. I was at the house today, and in fact it seems that the wire in question is actually more like a 4mm as it is definitely one size larger than some 2.5mm that I have just bought.

Well is it 4mm² or not?

Hi - I have a cable which is 2.5mm, with 3 +ves and 1 -ve (and 1 earth).

How about this - use one pair for the hob (i.e. 4mm +ve, -ve and 20A fuse), one pair for the oven and dishwasher (i.e. 4mm on 20A fuse).

1) Our domestic supply is AC, so the terms "positive" and "negative" are meaningless.
2) What kind of cable has 4 cores and one earth?

In this way, I should be almost legal!

If you count contravening the building regulations, offences for which a number of people have recently been fined several thousands of pounds "almost legal", then yes...

 

[TrueBlue]

2) What kind of cable has 4 cores and one earth?

A 4 core and earth one, I'd imagine.

 

[ban-all-sheds]

I have one earth cable, at least 2.5mm, more like a 4mm.

If I route all three earths (hob, oven, dishy) through this one is that OK?

No. Please stop now and call an electrician.

What is the best way to tell? With a micrometer? I have roughly measured the external diameter with a ruler which is almost 5mm, so I think 4mm is right.

Cable sizes are the cross-sectional areas of the conductors, not diameters. Please stop now and call an electrician.

My 5 conductor cable coming out of the wall needs pliers to bend it, so it must be larger than 2.5mm, thus 4mm, next size up?

1) 5-core cable sounds nothing like any cable I've ever heard of as being suitable for use for fixed wiring. Please stop now and call an electrician.
2) You are guessing at the size, and therefore guessing at the current carrying capacity, and therefore guessing that it won't catch fire. Please stop now and call an electrician.

In any case, with the 2 pairs together I know I have at least 5mm cable, quite possibly 8mm, with an earth of 4mm.

You know nothing of the sort. Please stop now and call an electrician.

 

[Steve]

You know nothing of the sort. Please stop now and call an electrician.

having just looked back, i agree.

 

[bernithebiker]

Hi ban-all-sheds ; some of your replies need clarification if I am to learn anything;

"I have one earth cable, at least 2.5mm, more like a 4mm.

If I route all three earths (hob, oven, dishy) through this one is that OK?

No. Please stop now and call an electrician. "

Why not? Should the earth be larger than 4mm?

bernithebiker wrote:
What is the best way to tell? With a micrometer? I have roughly measured the external diameter with a ruler which is almost 5mm, so I think 4mm is right.

Cable sizes are the cross-sectional areas of the conductors, not diameters. Please stop now and call an electrician.

If this is the case then I have AT LEAST a radius of 1mm in my cable, which would be 3.14mm2, so the cable can only be 4mm2 or greater. I will measure it exactly with a micrometer.

Quote:
My 5 conductor cable coming out of the wall needs pliers to bend it, so it must be larger than 2.5mm, thus 4mm, next size up?

1) 5-core cable sounds nothing like any cable I've ever heard of as being suitable for use for fixed wiring. Please stop now and call an electrician.
2) You are guessing at the size, and therefore guessing at the current carrying capacity, and therefore guessing that it won't catch fire. Please stop now and call an electrician.

This 5 core cable is surely related to 3 phase wiring. Although the house is monophase, the guy who put this in obviously decided to have some extra wire capacity by using this 5 core wire. There are 3 reds, 1 blue and 1 earth. My 'guess' re cable size is an educated one at least - the cable is for sure larger than 2.5mm2.

Quote:
In any case, with the 2 pairs together I know I have at least 5mm cable, quite possibly 8mm, with an earth of 4mm.

You know nothing of the sort. Please stop now and call an electrician.

Incorrect. Please see above.

 

[Adam_151]

This 5 core cable is surely related to 3 phase wiring. Although the house is monophase, the guy who put this in obviously decided to have some extra wire capacity by using this 5 core wire. There are 3 reds, 1 blue and 1 earth.

Incorrect. Please see above.

I've never heard of such a cable, why are the phases the same colour as each other?, and why is the neutral coded to a colour standard different from the rest that most likely didn't exist in this country when the cable was installed?

Not conduit with whatever scraps of cable he could find is it?

 

[Qedelec]

Please post the address of this property, so that we can make sure none of us accidentally purchases it in the future.
Judging by your posts, you have serious gaps in your electrical knowledge which are potentialy lethal.

Part P building regulations were enacted to attempt to ensure unsafe practices are eradicated. I am not niave enough to believe this will happen overnight, but not only does the work you propose reveal your lack of electrical understanding but could put any occupants in danger.

AS STATED EARLIER........CALL AN ELECTRICIAN you are out of your depth

 

[bernithebiker]

Just to reassure everyone that is totally freaking out, an electrician is on his way, but it takes at least a week to get one out round here.

I am simply after a temporary solution that will allow me to heat up some beans.

Sincere apologies for saying +ve and -ve - I will give them their correct names in future.

The wire in question (not conduit with scraps, no) is >2.5mm, suspect 4mm2, 5 solid cores, with 3 reds, 1 blue and 1 earth. Surely it is not beyond the realms of possibility that such a cable exists? If I get time I'll take a picture of it and post it up.

I still do not see what is so terribly wrong with putting the hob onto one 4mm pair which goes to a 20A fuse on the main board. If necessary I can upgrade this fuse to 32A.

Then the oven and dishy on the other 4mm pair, also on a 20A fuse.

Earths all connected up. I may even use my 32A and 2 x 16A trip switches at the kitchen for extra protection.

So, forgive my ignorance, but where exactly is the problem?

 

[TrueBlue]

Surely it is not beyond the realms of possibility that such a cable exists? If I get time I'll take a picture of it and post it up.

Such a cable does indeed exist, though it is unusual to be used in house hold wiring. There is nothing wrong with having a blue wire for the nuetral Adam_151. Go and take a look inside the nearest plug top.

bernithebiker, how can you adequately protect the cable if you don't even know what size it is?! There is a distinct difference in ratings between cable sizes. You can't just take a stab at it and hope for the best. You seem completely dissmissive about the earthing requirements in your installation. It is the cable you should be giving most thought too. you cannot increase the cable size ie 5mm/2 and not increase the earthing cable size. Where would you stop? Earth the whole house with a 2.5???

 

[ban-all-sheds]

Hi ban-all-sheds ; some of your replies need clarification if I am to learn anything;

"I have one earth cable, at least 2.5mm, more like a 4mm.

If I route all three earths (hob, oven, dishy) through this one is that OK?

No. Please stop now and call an electrician. "

Why not? Should the earth be larger than 4mm?

OK - "no" was, I admit, a quick and simple answer, guaranted to be safe.

You were talking about doubling up the live & neutral conductors, this giving you, for argument's sake, 8mm² with a 4mm² cpc. Such a combination would require you to carry out calculations to confirm that such a reduced size cpc was adequate.

It seemed easier all round to advise you not to bother, and stick to conventional cables.

But if you want to go ahead, you'll find details of the calculations here: http://www.tlc-direct.co.uk/Book/5.4.5.htm